Conventionally, petroleum refiners fractionate crude oil in a crude distillation zone to produce more desirable hydrocarbon fraction products such as vacuum gas oil (VGO). In general, further processing or additional treatments are required before the hydrocarbon fractions meet the necessary product specifications. It is often beneficial to selectively remove polycyclic aromatic hydrocarbon (PAH) compounds as these compounds are believed to be at least partially responsible for soot emissions from typical diesel engines and are believed to be coke precursors. PAH compounds are hydrocarbons containing two or more fused rings wherein at least one ring is aromatic. Specific examples include, but are not limited to, naphthalene, acenaphthene, pyrene, hexahydropyrene, indene, fluoroanthrene, and alkylated derivatives such as 7,12-dimethylbenzanthracene.
VGO is a typical feedstock for fluidized catalytic cracking (FCC) based upgrading processes. The contaminants in VGO such as sulfur, nitrogen, metals and polycyclic aromatics cause deactivation of the FCC catalyst, thereby decreasing gasoline and distillate yields on a per-pass basis. A significant portion of the contaminants are present as highly aromatic compounds. Sometimes the contaminant content of VGO feeds are reduced by hydrotreating the feed to remove nitrogen, metals, sulfur and PAHs. An example of PAH reduction by hydrotreating is U.S. Pat. No. 7,794,588. However, this process uses hydrogen, in a costly process step. Additionally, hydroprocessing of feeds reduced in contaminants is significantly easier than processing highly contaminated feeds.
This invention relates to a process to upgrade VGO feeds by selectively extracting aromatic compounds from them by treatment with certain phosphonium based ionic liquids. Removal of the aromatics from hydrocarbon fractions such as VGO will have a beneficial impact on downstream processing conditions. It can be envisioned that similar aromatic compounds could be extracted from other hydrocarbon streams as well.